Exemplary embodiments of the present invention relate to a method for operating an internal combustion engine having an exhaust emission control unit and to a device for operating an internal combustion engine having an exhaust emission control unit.
German patent document DE 10 2009 021 114 A1 describes a method for operating an air-compressing internal combustion engine, having an exhaust tract with an exhaust emission control unit that acts catalytically and/or by filtration. The combustion chambers of the internal combustion engine are supplied with fuel and a combustion gas, having an air fraction and a fraction of exhaust gas that is recirculated from the exhaust tract, which is provided for at least partial combustion of the fuel, the recirculated exhaust gas being suppliable to the combustion chambers with a low-pressure component via a low-pressure path that branches off from the exhaust tract downstream from the exhaust emission control unit, and with a high-pressure component via a high-pressure path that branches off from the exhaust tract upstream from an exhaust gas turbocharger turbine. An oxygen mass content in the combustion gas is at least approximately set to a predefinable setpoint value essentially by activating a low-pressure EGR valve situated in the low-pressure path and/or a sensor flap situated in the exhaust tract and a high-pressure EGR valve situated in the high-pressure path.
German patent document DE 10 2009 007 764 A1 describes a method for operating an internal combustion engine, having an exhaust emission control system with at least one exhaust emission control component which acts catalytically and/or by filtration. In conjunction with a cold start and/or a warm-up of the internal combustion engine, the internal combustion engine is operated using a cold start engine operating process with predefinable values for predefinable internal combustion engine operating variables. A quantity of HC stored in one or more of the at least one exhaust emission control component is estimated, and the cold start engine operating process is activated when the estimation shows that the quantity of stored HC exceeds a predefinable threshold value of the quantity of stored HC.
Exemplary embodiments of the present invention are directed to an improved method and device for operating an internal combustion engine having an exhaust emission control unit.
In the method of the invention for operating an internal combustion engine having an exhaust emission control unit which includes a particle filter in which, in conjunction with a cold start and/or a warm-up of the internal combustion engine, the internal combustion engine is operated using a cold start engine operating process with predefinable values for predefinable internal combustion engine operating variables. According to the invention the cold start and/or the warm-up of the internal combustion engine is/are controlled and/or regulated as a function of soot loading of a particle filter. As a result, controlled and particularly rapid temperature regulation of the exhaust emission control unit or at least of individual exhaust emission control components is made possible, resulting in particularly quick operational readiness of the exhaust emission control unit and particularly efficient exhaust emission control.
The temperature regulation of the exhaust emission control unit usually requires extreme temperature gradients in a heating phase directly after starting the internal combustion engine, in order to rapidly bring catalytically active components of the exhaust emission control unit, which are preferably present, into the temperature range in which they are active, and thus minimize the pollutant emissions. This increases the risk that soot stored in the particle filter may uncontrollably ignite. The resulting highly exothermic reactions may damage the particle filter or at least greatly intensify catalyst aging. This is reliably avoided with the present method. A cold start is understood to mean a start of the internal combustion engine under conditions in which the temperature of the coolant is below 50° C., in particular below 20° C., and/or a temperature within the exhaust emission control unit that is below 250° C., in particular below 200° C. Correspondingly, a warm-up is understood to mean an operation of the internal combustion engine subsequent to a cold start, in which the coolant and the exhaust emission control unit have not yet reached the mentioned temperatures. The warm-up operation is preferably ended directly after reaching the mentioned temperature values, and values of the operating variables intended for normal operation of the internal combustion engine are set.
The particle filter is particularly preferably heated to a predefinable operating temperature by controlled and/or regulated soot oxidation. During warm-up this optionally allows controlled removal of the soot stored in the particle filter, thus allowing a heating rate of the particle filter which is increased due to the released heat resulting from the soot oxidation, but which at the same time is controlled. The heating of the exhaust emission control unit may thus be advantageously assisted by controlled soot oxidation.
In a first embodiment, for an essentially unloaded particle filter, the exhaust emission control unit is heated to a predefinable operating temperature, using a predefinable maximum temperature gradient. This allows particularly rapid heating of the entire exhaust emission control unit, and thus a reduced warm-up time and resulting quick operational readiness and efficient exhaust emission control, in which ignition of the soot in the particle filter cannot occur. An “essentially unloaded particle filter” is understood to mean that the particle filter has a soot loading of less than 1 g per liter, in particular less than 0.5 g per liter, of particle filter volume. The maximum temperature gradient is suitably specified as a function of the highest possible value that is achievable under the prevailing conditions by setting appropriate values of internal combustion engine operating variables, and may have a value of approximately 100° C. to 500° C. per minute.
In a second embodiment, for a particle filter having soot loading exceeding a predefinable first threshold value, heating of the exhaust emission control unit during warm-up is carried out in such a way that a temperature in the particle filter is set below an ignition temperature of the stored soot. Uncontrolled ignition of the soot deposited in the particle filter is thus avoided during warm-up. The first threshold value for the soot loading corresponds to a comparatively high soot loading value of greater than approximately 5 g/L, in particular greater than 6 g/L. For these values of the soot loading, uncontrolled soot burnoff would release a very large quantity of heat within a short period of time, which due to limited heat dissipation would result in overheating of components of the exhaust emission control unit and in particular of the particle filter, which could damage or destroy the components or the particle filter. The warm-up is therefore carried out at a soot ignition temperature of approximately 550° C., so that the maximum temperature of the particle filter is below 550° C. during the warm-up operation.
In one preferred embodiment of the method, control and/or regulation of the internal combustion engine during warm-up is/are carried out in such a way that a lambda value of the combustion within the internal combustion engine is held below a predefinable value. The lambda value of the combustion is preferably held below approximately 1.2. The oxygen content in the exhaust gas may thus be held at a low value so that soot burnoff in the particle filter is prevented, or at least the rate of soot burnoff which could possibly take place unintentionally is limited to a noncritical value.
For a loaded particle filter, control and/or regulation of the internal combustion engine is/are particularly preferably carried out during warm-up in such a way that an exhaust gas mass flow is maximized. On the one hand this allows particularly rapid heating of components of the exhaust emission control unit, and on the other hand heat dissipation from the particle filter is increased, thus further reducing the risk of overheating due to soot burnoff.
Control and/or regulation of the internal combustion engine is/are advantageously carried out during warm-up in such a way that a start-stop operation of the internal combustion engine is deactivated. This reliably prevents switching off of the internal combustion engine during idling phases that occur during warm-up of the internal combustion engine, and thus prevents interruption of the operation of the internal combustion engine during the warm-up phase and resulting cooling down or cooling off of the exhaust emission control unit.
For a partially loaded particle filter having soot loading below a predefinable second threshold value, it is particularly preferred to carry out heating of the exhaust emission control unit to a predefinable operating temperature that is above an ignition temperature of the stored soot, using a predefinable maximum temperature gradient, resulting in ignition of the soot. Thus, during warm-up, soot is burned off in the particle filter, whose heat release further accelerates the heating of the exhaust emission control unit. This warm-up process is preferably carried out when the soot loading of the particle filter is greater than zero but less than approximately 4 g/L, in particular less than 3 g/L, at the beginning of the warm-up. In the warm-up process under discussion, with a partially loaded particle filter, temperature regulation is preferably carried out based on a temperature measurement performed at the output side of the particle filter. In contrast, in warm-up variants in which no soot burnoff in the particle filter is possible or provided, temperature regulation of the heating is carried out based on a guide temperature measured upstream from the particle filter. In addition, for a warm-up in which soot burnoff in the particle filter takes place or is provided, a start-stop operation with switching off of the internal combustion engine during idling operating phases may be permitted.
In one particularly advantageous embodiment, in a warmed-up internal combustion engine a particle filter loaded with soot may be regenerated to a partially loaded state having a predefinable value of the soot loading. The plurality of all mandatory particle filter regenerations is preferably carried out in such a way that a residual loading of soot remains in the particle filter after completion of the regeneration. Thus, on the one hand the duration of regeneration of the particle filter during normal operation is shortened. On the other hand, burnoff of the remaining soot in the particle filter may be advantageously assisted during warm-up which takes place with a partially loaded filter after switching off the internal combustion engine.
By use of the method according to the invention, on the one hand fuel consumption of the internal combustion engine during the regeneration of the particle filter and during warm-up is reducible. On the other hand, catalyst aging during the regeneration of the particle filter is reduced due to the decreased thermal load.
Furthermore, by means of the method according to the invention, dilution of the lubricant that is circulated in the internal combustion engine, which occurs during the regeneration of the particle filter as the result of a conventional post-injection strategy, is reduced.
Emissions loading as well as pollutant emissions of the internal combustion engine are advantageously reducible.
Effectiveness of soot deposition in the particle filter may be increased in a particularly advantageous manner by means of the residual soot that remains in the particle filter. As a result, more porous particle filter substrates, which in particular allow so-called selective catalytic reduction, may be used.
In the device for operating an internal combustion engine having an exhaust emission control unit with at least one exhaust emission control component that acts catalytically and/or by filtration, in which in conjunction with a cold start and/or a warm-up of the internal combustion engine, the internal combustion engine is operable using a cold start engine operating process with predefinable values for predefinable internal combustion engine operating variables, according to the invention the cold start and/or the warm-up of the internal combustion engine is/are controllable and/or regulatable as a function of soot loading of a particle filter of the exhaust emission control unit, soot loading of the particle filter being determinable based on a differential pressure measurement of an exhaust gas back pressure upstream and downstream from the particle filter, and/or based on a computation model, stored in a control unit, of soot loading of the particle filter as a function of operating states of the internal combustion engine which occur.